Braised Beef with Peppers (Zilzil Tibs)

1 pound unsalted butter 1 tablespoon chopped fresh ginger 1 teaspoon whole allspice berries 1 teaspoon fenugreek seeds 1 teaspoon dried oregano 1/2 teaspoon turmeric 6 black cardamom pods, crushed lightly with a knife blade 2 cloves garlic, coarsely chopped 1 small yellow onion, chopped